For example, a bit exchange device for exchanging a roller bit from a working space formed in a cutter head is disclosed in Japanese Patent No. 3139749 and Japanese Patent No. 4163965. The two bit exchange devices each have a rotating body with an opening at the front of cutter spokes. The roller bit is disposed in the opening of the rotating body. In replacement of cutters, the rotating body is rotated by 90° or 180° such that the opening of the rotating body faces an exchange opening near the side or back of the rotating body. The roller bit is then removed from the opening into the working space through the exchange opening, allowing replacement of the bit.